1. Technical Field
The present invention relates to a liquid ejecting apparatus such as an ink jet recording apparatus, and in particular relates to a liquid ejecting apparatus which includes a liquid ejecting head which ejects liquid from a nozzle by causing a pressure fluctuation in the liquid in a pressurizing chamber by driving a pressure generator, the pressure generator being driven by applying a driving waveform to the pressure generator.
2. Related Art
A liquid ejecting apparatus is an apparatus which includes a liquid ejecting head, and ejects (discharges) various types of liquid from the liquid ejecting head. As examples of the liquid ejecting apparatus, there is an image recording apparatus such as an ink jet printer, or an ink jet plotter. However, in recent years, the liquid ejecting apparatus is also applied to various manufacturing apparatuses by utilizing an advantage of accurate landing of liquid of an extremely small amount in a predetermined position. For example, the liquid ejecting apparatus can be applied to a display manufacturing apparatus which manufactures a color filter such as a liquid crystal display, an electrode forming apparatus which forms an electrode of an organic electro luminescence (EL) or a field emission display (FED), and a chip manufacturing apparatus which manufactures a biochip. In addition, liquid ink is ejected from a recording head for the image recording apparatus, and a solution of each color material of red (R), green (G), and blue (B) is ejected from a color material ejecting head for the display manufacturing apparatus. In addition, a liquid electrode material is ejected from an electrode material ejecting head for the electrode forming apparatus, and a solution of a bio organic matter is ejected from the living body organic matter ejecting head for the chip manufacturing apparatus.
Here, the above described liquid ejecting head causes a pressure fluctuation in liquid in a pressurizing chamber which communicates with a nozzle by driving a pressure generator, and causes the liquid to be ejected from the nozzle using the pressure fluctuation. In addition, as the pressure generator, a piezoelectric element which is deformed when a driving signal (driving voltage) is supplied is preferably used. In addition, as the driving signal which ejects liquid, a so-called ejection driving pulse with a trapezoidal wave (driving voltage waveform) is used since it is possible to eject liquid with high precision. The trapezoidal wave includes an expansion element which causes the pressurizing chamber to expand by being changed from a reference potential to an expansion potential which is lower than the reference potential, and a contraction element which causes the pressurizing chamber to be contracted by being changed from the expansion potential to the reference potential are used. In addition to the ejection driving pulse, a minute vibration driving pulse is included as part of the driving signal. The minute vibration driving pulse causes liquid in the pressurizing chamber to be vibrated (so-called minute vibration operation) to the extent that liquid is not caused to be ejected, in order to reduce thickening of a meniscus in a nozzle in which liquid is not ejected (for example, refer to JP-A-2010-264689). In the minute vibration driving pulse, a trapezoidal wave is used in which a voltage change from the reference potential is smaller than that of the ejection driving pulse. When such a minute vibration driving pulse is applied to a piezoelectric element, the piezoelectric element is heated, liquid in the pressurizing chamber is heated, and the liquid in the pressurizing chamber is agitated. The minute vibration driving using such a minute vibration driving pulse is performed with respect to a nozzle (in which ejection of liquid is not performed in the middle of liquid ejection processing) so that a variation in ejection property (amount, flying speed, or the like of ejected liquid) between an oft-used nozzle in which ejection of liquid is performed a relatively large number of times, and thickening of the nozzle is suppressed due to heating of the piezoelectric element and a less-used nozzle in which ejection of liquid is performed a relatively small number of times, and thickening of the nozzle in progress is suppressed.
Meanwhile, it is known that displacement amount (amount of deformation) of the piezoelectric element with respect to an applied driving voltage has a non-linear property (specifically, a hysteresis property). For example, in a piezoelectric property of a piezoelectric element which is exemplified in FIG. 5, a non-linear region in which a ratio of the displacement amount to the driving voltage is small is present on both vertical sides (low voltage side and high voltage side) of the linear region in which the ratio of the displacement amount to the driving voltage is large. For this reason, when liquid to be reliably ejected using a trapezoidal wave which is the driving voltage waveform, and a pressure fluctuation in the pressurizing chamber is desired to be as large as possible, a reference potential of the trapezoidal wave is set to a potential corresponding to the non-linear region on the high voltage side, and an expansion potential is set to a potential corresponding to the non-linear region on the low voltage side. It is possible to make the displacement amount of the piezoelectric element large by including the linear region in a voltage changing area of the driving voltage in this manner, and for example, it is possible to eject liquid of high viscosity (such as UV ink which is cured when being irradiated with a UV ray (light) with high precision).
However, when the reference potential is set to be high in order to make the displacement amount of the piezoelectric element large, there is a concern that it may not be possible to sufficiently reduce (suppress) thickening using a minute vibration operation. Specifically, since an amount of change in voltage of the minute vibration driving pulse is smaller than that of the ejection driving pulse, it is not possible to sufficiently use the linear region when the reference potential becomes high, and the displacement amount due to the piezoelectric element is not sufficient. That is, the higher the reference potential, the greater the ratio of the non-linear region to the voltage changing area of the minute vibration driving pulse, and the smaller the displacement amount of the piezoelectric element. Due to this, it is not possible to sufficiently agitate liquid in the pressurizing chamber, and to sufficiently heat liquid in the pressurizing chamber, since an amount of heat using the piezoelectric element decreases. As a result, viscosity of liquid becomes different between a nozzle in which ejection of liquid is performed relatively many times and a nozzle in which ejection of liquid is performed relatively few times, and a variation occurs in ejection properties such as an amount, or a flying speed of liquid ejected from a nozzle. In particular, since a ratio of viscosity of UV ink which is changed due to a change in temperature is large compared to normal ink, the variation in the above described ejection property becomes significant.